The invention relates to a breaking device for a low voltage molded case multipole circuit breaker, comprising a rotary switching bar guided in rotation around a first transverse fixed axis by means of bearings arranged in the case, said first axis being perpendicular to the longitudinal direction of each pole, which comprises;
a pair of stationary contacts connected to the connection terminals;
a double-break rotary contact extending in a housing of the bar in the longitudinal direction of the pole, and having opposing contact parts cooperating with the stationary contacts in the closed position;
a pair of springs arranged inside the housing of the bar to cooperate with the rotary contact ensuring a predetermined contact pressure of the contact parts on the stationary contacts.
The use of a double-break rotary contact in a circuit breaker enables two arcs to be connected in series favoring a high breaking capacity. In a hyperstatic system with full rotation guiding of the movable contact, the problem of uniform distribution of the contact pressure on the two stationary contacts arises. A solution to this problem is proposed in the document U.S. Pat. No. 4,649,247, in which the centre part of the rotary contact comprises an oblong hole slotted onto a fixed support rod to form a guiding system having a degree of freedom in translation. The fixed support rod is cylindrical in shape and is mounted coaxially in the bar, so that the rotary contact can move slightly in the direction perpendicular to the longitudinal axis of the pole to ensure a balanced contact pressure at the level of the two breaking gaps. The diameter of the rod corresponds appreciably to the width of the oblong hole, and any movement of the rotary contact in the longitudinal direction is rendered impossible. The longitudinal positioning of the rotary contact is accurately determined by the support rod, which imposes stringent manufacturing tolerances.
In the double-break rotary switch according to the document DE-OS-2,845,950, the contact pressure springs do not ensure efficient self-centering of the movable contact in the longitudinal extension direction of the connection terminals. The positioning of the movable contact with respect to the stationary contacts is liable to be modified in the course of the life-time of the switch. This results in a longitudinal offset of the contacts detrimental to breaking of the arc.
The object of the invention consists in simplifying the assembly of a double-break rotary contact on the switching bar of a molded insulating case circuit breaker.